1,018 research outputs found
Perspectives on safety culture
Overviewing selected elements from the literature, this paper locates the notion of safety culture within its parent concept of organisational culture. A distinction is drawn between functionalist and interpretive perspectives on organisational culture. The terms ‘culture’ and ‘climate’ are clarified as they are typically applied to organisations and to safety. A contrast is drawn between strategic top down and data-driven bottom up approaches to human factors as an illustrative aspect of safety. A safety case study is used to illustrate two measurement approaches. Key issues for future study include valid measurement of safety culture and developing methods to adequately represent mechanisms through which safety culture might influence, and be influenced by, other safety factors
Triple oxygen isotopic composition of the high-<sup>3</sup>He/<sup>4</sup>He mantle
Measurements of Xe isotope ratios in ocean island basalts (OIB) suggest that Earth’s mantle accreted heterogeneously, and that compositional remnants of accretion are sampled by modern, high-3He/4He OIB associated with the Icelandic and Samoan plumes. If so, the high-3He/4He source may also have a distinct oxygen isotopic composition from the rest of the mantle. Here, we test if the major elements of the high-3He/4He source preserve any evidence of heterogeneous accretion using measurements of three oxygen isotopes on olivine from a variety of high-3He/4He OIB locations. To high precision, the Δ17O value of high-3He/4He olivines from Hawaii, Pitcairn, Baffin Island and Samoa, are indistinguishable from bulk mantle olivine (Δ17OBulk Mantle − Δ17OHigh 3He/4He olivine = −0.002 ± 0.004 (2 × SEM)‰). Thus, there is no resolvable oxygen isotope evidence for heterogeneous accretion in the high-3He/4He source. Modelling of mixing processes indicates that if an early-forming, oxygen-isotope distinct mantle did exist, either the anomaly was extremely small, or the anomaly was homogenised away by later mantle convection.
The δ18O values of olivine with the highest 3He/4He ratios from a variety of OIB locations have a relatively uniform composition (∼5‰). This composition is intermediate to values associated with the depleted MORB mantle and the average mantle. Similarly, δ18O values of olivine from high-3He/4He OIB correlate with radiogenic isotope ratios of He, Sr, and Nd. Combined, this suggests that magmatic oxygen is sourced from the same mantle as other, more incompatible elements and that the intermediate δ18O value is a feature of the high-3He/4He mantle source. The processes responsible for the δ18O signature of high-3He/4He mantle are not certain, but δ18O–87Sr/86Sr correlations indicate that it may be connected to a predominance of a HIMU-like (high U/Pb) component or other moderate δ18O components recycled into the high-3He/4He source
DCC dynamics with the SU(3) linear sigma model
The SU(3) extension of the linear sigma model is employed to elucidate the
effect of including strangeness on the formation of disoriented chiral
condensates. By means of a Hartree factorization, approximate dispersion
relations for the 18 scalar and pseudoscalar meson species are derived and
their self-consistent solution makes it possible to trace out the thermal path
of the two order parameters as well as delineate the region of instability
within which spontaneous pair creation becomes possible. The results depend
significantly on the employed sigma mass, with the highest values yielding the
largest regions of instability. An approximate solution of the equations of
motion for the order parameter in scenarios emulating uniform scaling
expansions show that even with a rapid quench only the pionic modes grow
unstable. Nevertheless, the rapid and oscillatory relaxation of the order
parameters leads to enhanced production of both pions and (to a lesser degree)
kaons.Comment: 29 pages, RevTeX, 11 postscript figures, discussion about anomaly
term adde
Breakup Reactions of 11Li within a Three-Body Model
We use a three-body model to investigate breakup reactions of 11Li (n+n+9Li)
on a light target. The interaction parameters are constrained by known
properties of the two-body subsystems, the 11Li binding energy and
fragmentation data. The remaining degrees of freedom are discussed. The
projectile-target interactions are described by phenomenological optical
potentials. The model predicts dependence on beam energy and target,
differences between longitudinal and transverse momentum distributions and
provides absolute values for all computed differential cross sections. We give
an almost complete series of observables and compare with corresponding
measurements. Remarkably good agreement is obtained. The relative neutron-9Li
p-wave content is about 40%. A p-resonance, consistent with measurements at
about 0.5 MeV of width about 0.4 MeV, seems to be necessary. The widths of the
momentum distributions are insensitive to target and beam energy with a
tendency to increase towards lower energies. The transverse momentum
distributions are broader than the longitudinal due to the diffraction process.
The absolute values of the cross sections follow the neutron-target cross
sections and increase strongly for beam energies decreasing below 100 MeV/u.Comment: 19 pages, 14 figures, RevTeX, psfig.st
Crystal chemistry search of multiferroics with the stereochemically active lone pair
On the basis of our previous studies of magnetoelectric ordering of BiFeO3,
TbMnO3, TbMn2O5 and BiMn2O5 we formulate the crystal chemistry criteria for the
search of multiferroics and reveal potential multiferroics Pb2Cu(OH)4Cl2,
Pb5Cr3F19, Mn(SeO3){\dot}H2O and BiPbSr2MnO6 each containing the ion with a
lone pair.Comment: 4 pages, 8 figures,submitted to J Supercond Nov Mag
Quantum curves for Hitchin fibrations and the Eynard-Orantin theory
We generalize the topological recursion of Eynard-Orantin (2007) to the
family of spectral curves of Hitchin fibrations. A spectral curve in the
topological recursion, which is defined to be a complex plane curve, is
replaced with a generic curve in the cotangent bundle of an arbitrary
smooth base curve . We then prove that these spectral curves are
quantizable, using the new formalism. More precisely, we construct the
canonical generators of the formal -deformation family of -modules
over an arbitrary projective algebraic curve of genus greater than ,
from the geometry of a prescribed family of smooth Hitchin spectral curves
associated with the -character variety of the fundamental
group . We show that the semi-classical limit through the WKB
approximation of these -deformed -modules recovers the initial family
of Hitchin spectral curves.Comment: 34 page
Deterministic and stochastic descriptions of gene expression dynamics
A key goal of systems biology is the predictive mathematical description of
gene regulatory circuits. Different approaches are used such as deterministic
and stochastic models, models that describe cell growth and division explicitly
or implicitly etc. Here we consider simple systems of unregulated
(constitutive) gene expression and compare different mathematical descriptions
systematically to obtain insight into the errors that are introduced by various
common approximations such as describing cell growth and division by an
effective protein degradation term. In particular, we show that the population
average of protein content of a cell exhibits a subtle dependence on the
dynamics of growth and division, the specific model for volume growth and the
age structure of the population. Nevertheless, the error made by models with
implicit cell growth and division is quite small. Furthermore, we compare
various models that are partially stochastic to investigate the impact of
different sources of (intrinsic) noise. This comparison indicates that
different sources of noise (protein synthesis, partitioning in cell division)
contribute comparable amounts of noise if protein synthesis is not or only
weakly bursty. If protein synthesis is very bursty, the burstiness is the
dominant noise source, independent of other details of the model. Finally, we
discuss two sources of extrinsic noise: cell-to-cell variations in protein
content due to cells being at different stages in the division cycles, which we
show to be small (for the protein concentration and, surprisingly, also for the
protein copy number per cell) and fluctuations in the growth rate, which can
have a significant impact.Comment: 23 pages, 5 figures; Journal of Statistical physics (2012
Supersymmetric solutions of PT-/non-PT-symmetric and non-Hermitian Screened Coulomb potential via Hamiltonian hierarchy inspired variational method
The supersymmetric solutions of PT-symmetric and Hermitian/non-Hermitian
forms of quantum systems are obtained by solving the Schrodinger equation for
the Exponential-Cosine Screened Coulomb potential. The Hamiltonian hierarchy
inspired variational method is used to obtain the approximate energy
eigenvalues and corresponding wave functions.Comment: 13 page
Ultrafast Nonlinear Optical Response of Strongly Correlated Systems: Dynamics in the Quantum Hall Effect Regime
We present a theoretical formulation of the coherent ultrafast nonlinear
optical response of a strongly correlated system and discuss an example where
the Coulomb correlations dominate. We separate out the correlated contributions
to the third-order nonlinear polarization, and identify non-Markovian dephasing
effects coming from the non-instantaneous interactions and propagation in time
of the collective excitations of the many-body system. We discuss the
signatures, in the time and frequency dependence of the four-wave-mixing (FWM)
spectrum, of the inter-Landau level magnetoplasmon (MP) excitations of the
two-dimensional electron gas (2DEG) in a perpendicular magnetic field. We
predict a resonant enhancement of the lowest Landau level (LL) FWM signal, a
strong non-Markovian dephasing of the next LL magnetoexciton (X), a symmetric
FWM temporal profile, and strong oscillations as function of time delay, of
quantum kinetic origin. We show that the correlation effects can be controlled
experimentally by tuning the central frequency of the optical excitation
between the two lowest LLs.Comment: 21 pages, 10 figure
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
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